Motor vehicle suspension systems are configured so that the wheels are able to follow elevational changes in the road surface as the vehicle travels therealong. When a rise in the road surface is encountered, the suspension responds in “jounce” in which the wheel is able to move upwardly relative to the frame of the vehicle. On the other hand, when a dip in the road surface is encountered, the suspension responds in “rebound” in which the wheel is able to move downwardly relative to the frame of the vehicle. In either jounce or rebound, a spring (i.e., hydraulic fluid, leaf, torsion, etc.) is incorporated at the wheel in order to provide a resilient response to the respective vertical movements with regard to the vehicle frame. However, in order to prevent wheel bouncing and excessive vehicle body motion, a shock absorber is placed at the wheel to dampen wheel bounce. Additionally, when the limit of jounce is encountered, it is customary to provide a maximum jounce impact absorber in the form of a bumper cushion.
Referring now to FIGS. 1 through 1B, components of a conventional suspension system 10 are depicted which allow for jounce and rebound at a wheel of the subject motor vehicle 12.
Firstly with regard to FIG. 1, a control arm 14 is pivotally mounted with respect to the frame 16, wherein, in the depicted example, a torsion spring 18 is utilized to provide resilient response for the jounce and rebound of the control arm relative to the frame. To provide control over the rate of jounce and rebound, a damper in the form of a shock absorber 20 is connected pivotally at one end to the frame 16 and connected pivotally at the other end to the control arm 14. Alternatively, a damper in the form of a strut may be used in the suspension system, as for example disclosed in U.S. Pat. No. 5,467,971. To provide cushioning in the event a maximum jounce occurs, a jounce bumper cushion 22 is mounted to the frame 16 which is resiliently compressed by movement of the control arm as jounce approaches its maximum.
Referring next to FIG. 1A, the internal components and operational aspects of a conventional shock absorber 20′ (a remote reservoir high pressure gas type shock absorber being shown merely by way of example) can be understood. A valved piston 30 is reciprocably movable within a shock cylinder 32. A shock rod 34 is attached to the valved piston 30 and is guided by a shock rod guide 36 at one end of the shock cylinder 32. Below the valved piston 30 and above the shock rod guide 36 is a mutually interacting rebound limiter 38. The instantaneous position of the valved piston 30 within the shock cylinder 32 defines a first interior portion 32F and a second interior portion 32S of the interior of the shock cylinder. In the example depicted at FIG. 1A, the pressurization in the first and second interior portions 32F, 32S is provided by an hydraulic fluid O which is pressurized by pressurized gas, preferably nitrogen, G acting on a divider piston 40 of an hydraulic fluid reservoir cylinder 42, wherein a tube 44, including a base valve 44V, connects the hydraulic fluid between the hydraulic fluid reservoir cylinder and the first interior portion. In operation, as the control arm undergoes jounce, the hydraulic fluid is displaced from the first interior portion into the hydraulic fluid reservoir cylinder, causing the pressure of the nitrogen gas to increase as its volume decreases and thereby causing an increased hydraulic pressure on the valved piston 30 in a direction toward the shock rod guide. Hydraulic fluid is able to directionally meter through valving 46 of the valved piston 30 in a manner which provides damping.
Referring next to FIG. 1B, the internal structure of a conventional jounce bumper cushion 22 can be understood. An optional skin 50 of a compliant material (i.e., having energy absorbing or damping properties) may, or may not, overlay an interior of resilient elastomeric material 52, which may be for example a rubber, rubber-like material, or micro-cellular urethane. In operation as the control arm approaches maximum jounce, the jounce bumper cushion 22 compresses, delivering a reaction force on the control arm which increases with increasing compression so as to minimize the severity of impact of the control arm with respect to the frame at the limit of jounce. Immediately following the jounce, the rebound involves the energy absorbed by the compression of the conventional bumper cushion being delivered resiliently back to the suspension.
In the art of motor vehicle suspension systems, it is known that a conventional jounce bumper cushion and related dampers can show wear. It is also known that when the energy absorbed from a particular bump or dip exceeds the capacity of a conventional jounce bumper cushion, a hard mechanical stop is engaged. This abrupt transfer of jounce force and energy to the frame manifests itself in the passenger compartment as a sharp jolt, which can create load management issues in addition to the discomfort of a rough ride.
What remains needed in the art is a multistage jounce bumper, which can absorb an enhanced level of suspension system jounce force and energy as compared to a conventional jounce bumper cushion, while improving the feel and control of the ride.